For selection of a diode for a particular application,the data sheets provided by by the device manufacture must be consulted.
Most data sheets start off with the devices type number at the top of the sheet,a short descriptive title and a list of major application of the device.The information is usually followed by mechanical data in the form of illustration showing the package shape and dimensions.The absolute maximum ratings of the diode at 25°C are listed next.These are maximum voltages,currents,temperature etc.,that the device can bear/carry without breaking down. It is very important,for the safe operation of the device,the maximum ratings given in the data sheets are never exceeded.For reliability the maximum ratings should not even be approached.Also, the maximum rating must be adjusted downward for operation at temperature exceeding 25°C.Following the absolute maximum ratings,there is normally a complete list of electrical characteristics for the devices.Again,these are specified at 25°C, and allowances are necessary for variation of temperature.
some of the important parameters are considered below:
1.Peak reverse voltage or peak of voltage,VR or VRM.This is the absolute peak of voltage that must be applied in reverse across the diode.
2.steady-state forward current,I0 or IF.This is the maximum current that may be passed continuously through the diode.
3.peak forward surge current,IFM (surge).The surge current is very much higher than the normal maximum forward current.This rating defines the maximum value and the time interval for such surge in current level.It is a current that may flow briefly when a circuit is first switched on.
4.peak repetitive forward current is the maximum instantaneous value of repetitive forward current.This rating defines the maximum value and the time interval for such surge in current level.It is a current that level can be higher than the continuous level.
5.Average rectified current.A half-wave-rectifier signal has an average value defines y Iav=0.318 Ipeak .The average current rating is lower than the continuous or peak repetitive forward currents because a half-wave current waveform will have instantaneous values much higher than the average value.
6.static maximum voltage drop,VF(max).This is the maximum forward voltage drop for a given forward current and device temperature.
7.Continuous power dissipation at 25°C,P.This is the maximum power that the device can safely dissipate on a continuous basis in free air. This rating must be downgraded for operation at higher temperature,and may be upgraded when the device is mounted on a heat sink.
8.Reverse recovery time,trr .This is the maximum time for the device to switch from on to off.
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